1. Technical Field
The present disclosure relates to apparatuses for generating ultra violet light.
2. Related Art
The miniaturization and increased levels of integration of semiconductor integrated circuits have led to a demand for increases in the resolutions of semiconductor exposure devices. Semiconductor exposure devices will be referred to simply as “exposure devices” herein after. Accordingly, advances are being made in the reduction of the wavelengths of light outputted from exposure light sources. G as laser devices are being used as exposure light sources instead of conventional mercury lamps. At present, a KrF excimer laser device that outputs ultra violet light having a wavelength of 248 nm and an ArF excimer laser device that outputs ultra violet light having a wavelength of 193 nm are being used as gas laser devices for exposure.
Immersion exposure, in which the apparent wavelength of an exposure light source is reduced by filling a gap between the projection lens of an exposure device and a wafer with a liquid and changing the refractive index of the gap, is being researched as a next-generation exposure technique. In the case where immersion exposure is carried out using an ArF excimer laser device as the exposure light source, the wafer is irradiated with ultra violet light having a wavelength of 134 nm within the liquid. This technique is called ArF immersion exposure. ArF immersion exposure is also sometimes called “ArF immersion lithography”.
Because the spectral line width when a KrF or ArF excimer laser device oscillates naturally is wide at approximately 350 to 400 pm, chromatic aberration occurs in the laser beam (ultra violet light) projected in a reduced manner onto the wafer by the projection lens in the exposure device, which in turn causes the resolution to drop. Accordingly, it is necessary to narrow the spectral line width of the laser beam outputted from the gas laser device until the chromatic aberration reaches a level that can be ignored. The spectral line width is also sometimes called the “spectral width”. For this reason, a line narrow module having a line narrowing element is provided within the laser resonator of the gas laser device, and the narrowing of spectral width is being realized using this line narrow module. Note that the line narrowing element may be an etalon, a grating, or the like. A laser device that narrows the spectral width in this manner is called a narrow-band laser device.